A wide variety of rotary cone drill bits are used for drilling earth boreholes for the exploration and production of oil and gas and for mining operations. Such drill bits often employ multiple rolling cutter cone assemblies, also known as rotary cutter cone assemblies. The cutter cone assemblies are typically mounted on respective spindles or journals that extend downwardly and inwardly relative to an axis extending through an associated bit body so that conical surfaces of the cutter cone assemblies tend to roll on the bottom of a borehole in contact with the adjacent earth formation. Cutter cone assemblies generally have circumferential rows of milled teeth or inserts to scrape, cut and/or gouge the formation at the bottom of the borehole. Forming teeth on a generally conically shaped forging by milling is often a relatively expensive, time consuming process. Multiple milling steps are frequently required to form each tooth of a typical milled teeth cutting structure.
Milled teeth on conventional cone assemblies tend to wear in those areas that engage the bottom and side wall of a borehole during drilling operations. Milled teeth typically have a generally pyramidal configuration with a trapezoidal cross-section extending from the exterior surface of the associated cutter cone assembly. The generally pyramidal configuration is formed during the milling operation to provide sufficient structural support with adjacent portions of the associated cutter cone assembly. As a result of slanted surfaces associated with the generally pyramidal, milled teeth will generally become more blunt from abrasion, erosion and wear during drilling operations. Unless additional weight is applied to the associated rotary cone drill bit, the penetration rate will generally decrease as the area of contact increases with the bottom of a borehole resulting from the wear of milled teeth having a generally pyramidal configuration.
The service life of a rotary cone drill bit having cutter cone assemblies with respective milled teeth cutting structures may be improved by the addition of abrasion and wear resistant materials to selected wear areas of each tooth. The addition of abrasion and wear resistant materials to milled teeth is sometimes referred to as "hardfacing." In a hardfacing operation, abrasion and wear resistant material is applied to the teeth to provide not only a wear resistant surface to reduce the rate at which each milled tooth is worn off, but also to maintain sharper cutting edges as the teeth wear.
Examples of rotary cone drill bits having cutter cone assemblies with respective milled teeth cutting structures are shown in U.S. Pat. No. 5,579,856 entitled Gage Surface and Method for Milled Tooth Cutting Structure and U.S. Pat. No. 2,533,256 entitled Drill Cutter. Such drill bits may sometimes be referred to as "steel tooth" drill bits or "milled tooth" drill bits.
Conventional cutter cone assemblies with milled teeth often include multiple rows of teeth disposed on the respective conical surfaces. Such cutter cone assemblies somewhat resemble spur gears or bevel gears with interlocking or intermeshing teeth. Variations of these patterns include skewing the teeth similar to that of a spiral bevel gear, or even an alternating skew to produce a herringbone effect. Another accepted version of a drill bit is an interrupted circumferential disc having a resulting appearance of teeth aligned end to end around the periphery of the associated cutter cone assembly.